Controller for increasing efficiency of a power converter and a related method thereof

ABSTRACT

A controller for increasing efficiency of a power converter includes a comparison module and a gate signal generation unit. The comparison module is used for generating a detection voltage according to a direct current (DC) input voltage of a primary side of the power converter, and comparing the detection voltage with a predetermined value to generate a comparison result. The gate signal generation unit is used for changing a sink current flowing through a gate pin of the controller according to the comparison result, wherein the gate pin of the controller is coupled to a power switch of the primary side of the power converter.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a division of U.S. patent application Ser. No. 15/232,813, filedon 2016 Aug. 10.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a controller for increasing efficiencyof a power converter and a related method thereof, and particularly to acontroller and a related method thereof that can change a currentflowing through a gate pin of the controller coupled to a power switchof the power converter to increase efficiency of the power converter.

2. Description of the Prior Art

The US Department of Energy has requested that efficiency of a nextgeneration external power adapter needs to meet the VI level powerspecification. To make the efficiency of the next generation externalpower adapter meet the VI level power specification, a designer of apower converter applied to the next generation external power adaptermay need to significantly change a design of the power converterprovided by the prior art, resulting in cost of the power converterapplied to the next generation external power adapter beingsignificantly increased. In addition, if a sink current flowing througha gate pin of a controller is increased (wherein the gate pin of thecontroller is coupled to a power switch of a primary side of the powerconverter), efficiency of the power converter can be increased withoutsignificant increase of the cost of the power converter. However,electromagnetic interference of the power converter will be increaseddue to increase of the sink current flowing through the gate pin of thecontroller. Therefore, how to increase the efficiency of the powerconverter without significant increase of the electromagneticinterference of the power converter has become an important issue of thedesigner of the power converter.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a controller forincreasing efficiency of a power converter. The controller includes acomparison module and a gate signal generation unit. The comparisonmodule is used for generating a detection voltage according to a directcurrent (DC) input voltage of a primary side of the power converter, andcomparing the detection voltage with a predetermined value to generate acomparison result. The gate signal generation unit is used for changinga sink current flowing through a gate pin of the controller according tothe comparison result, wherein the gate pin is coupled to a power switchof the primary side of the power converter.

Another embodiment of the present invention provides a controller forincreasing efficiency of a power converter. The controller includes anenable signal generation unit and a gate signal generation unit. Theenable signal generation unit is used for generating an enable signalcorresponding to a duty cycle of a gate control signal according to a DCinput voltage corresponding to a primary side of the power converter anda feedback voltage corresponding to a secondary side of the powerconverter, wherein the feedback voltage corresponds to an output voltageof the secondary side of the power converter. The gate signal generationunit is used for changing a sink current flowing through a gate pin ofthe controller according to the enable signal, wherein the gate pin iscoupled to a power switch of the primary side of the power converter,and the gate signal generation unit is further used for generating agate control signal to the power switch.

Another embodiment of the present invention provides a method forincreasing efficiency of a power converter, wherein a controller appliedto the method includes a high voltage pin, a comparison module, and agate signal generation unit, and the comparison module includes adetection voltage generation unit and a comparator. The method includesthe high voltage pin receiving a DC input voltage from a primary side ofthe power converter; the detection voltage generation unit generating adetection voltage according to the DC input voltage; the comparatorcomparing the detection voltage with a predetermined value to generate acomparison result; and the gate signal generation unit changing a sinkcurrent flowing through a gate pin of the controller according to thecomparison result.

Another embodiment of the present invention provides a method forincreasing efficiency of a power converter, wherein a controller appliedto the method includes an auxiliary pin, a comparison module, and a gatesignal generation unit, and the comparison module includes a detectionvoltage generation unit and a comparator. The method includes theauxiliary pin receiving an auxiliary voltage from a voltage dividercoupled to an auxiliary winding of the power converter, wherein theauxiliary voltage corresponds to a DC input voltage; the detectionvoltage generation unit generating a detection voltage according to theauxiliary voltage; the comparator comparing the detection voltage with apredetermined value to generate a comparison result; and the gate signalgeneration unit changing a sink current flowing through a gate pin ofthe controller according to the comparison result, wherein the gate pinis coupled to a power switch of a primary side of the power converter.

Another embodiment of the present invention provides a method forincreasing efficiency of a power converter, wherein a controller appliedto the method includes a high voltage pin, an enable signal generationunit, and a gate signal generation unit. The method includes the highvoltage pin receiving a DC input voltage from a primary side of thepower converter; the enable signal generation unit generating an enablesignal corresponding to a duty cycle of a gate control signal accordingto the DC input voltage and a feedback voltage corresponding to asecondary side of the power converter, wherein the feedback voltagecorresponds to an output voltage of the secondary side of the powerconverter; and the gate signal generation unit changing a sink currentflowing through the gate pin of the controller according to the enablesignal.

The present invention provides a controller for increasing efficiency ofa power converter and a related method thereof. The controller and themethod utilize a comparison module to generate a detection voltageaccording to a DC input voltage corresponding to a primary side of thepower converter and to compare the detection voltage with apredetermined value to generate a comparison result, and utilize a gatesignal generation unit to increase a sink current flowing through a gatepin of the controller according to the comparison result. In addition,the controller and the method can also utilize an enable signalgeneration unit to generate an enable signal corresponding to a dutycycle of agate control signal according to the DC input voltagecorresponding to the primary side of the power converter and a feedbackvoltage corresponding to a secondary side of the power converter, andutilize the gate signal generation unit to increase the sink currentflowing through the gate pin of the controller according to the enablesignal. Therefore, when the sink current flowing through the gate pin ofthe controller is increased and the gate control signal is changed fromhigh to low, because the sink current flowing through the gate pin ofthe controller is increased, the gate control signal can be quicklychanged from high to low. That is to say, a power switch of the primaryside of the power converter can be switched quickly, resulting in theefficiency of the power converter being better. Although when the powerswitch of the primary side of the power converter is switched quickly,electromagnetic interference of the power converter is increased, theelectromagnetic interference of the power converter can be eliminatedeasily because the DC input voltage is a low voltage. Therefore,compared to the prior art, the present invention can increase theefficiency of the power converter without significant increase of costof the power converter

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a controller for increasing efficiencyof a power converter according to a first embodiment of the presentinvention.

FIG. 2 is a diagram illustrating the gate control signal being quicklychanged from high to low when the sink current flowing through the gatepin of the controller is increased.

FIG. 3 is a diagram illustrating a controller for increasing theefficiency of the power converter according to a second embodiment ofthe present invention.

FIG. 4 is a diagram illustrating a controller for increasing theefficiency of the power converter according to a third embodiment of thepresent invention.

FIG. 5 is a flowchart illustrating a method for increasing efficiency ofa power converter according to a fourth embodiment of the presentinvention.

FIG. 6 is a flowchart illustrating a method for increasing efficiency ofa power converter according to a fifth embodiment of the presentinvention.

FIG. 7 is a flowchart illustrating a method for increasing efficiency ofa power converter according to a sixth embodiment of the presentinvention.

DETAILED DESCRIPTION

Please refer to FIG. 1. FIG. 1 is a diagram illustrating a controller200 for increasing efficiency of a power converter 100 according to afirst embodiment of the present invention. As shown in FIG. 1, thecontroller 200 includes a high voltage pin 202, a comparison module 204,and a gate signal generation unit 206, wherein the comparison module 204includes a detection voltage generation unit 2042 and a comparator 2044.As shown in FIG. 1, the high voltage pin 202 can receive a directcurrent (DC) input voltage DCIV from a primary side PRI of the powerconverter 100, wherein the DC input voltage DCIV corresponds to analternating current (AC) input voltage ACIV inputted to the powerconverter 100. The detection voltage generation unit 2042 of thecomparison module 204 is coupled to the high voltage pin 202 forgenerating a detection voltage VD according to the DC input voltage DCIVof the primary side PRI of the power converter 100, wherein thedetection voltage VD is a divided voltage of the DC input voltage DCIV.In addition, the comparator 2044 of the comparison module 204 is usedfor comparing the detection voltage VD and a predetermined value PV togenerate a comparison result CR. That is to say, when the detectionvoltage VD (the divided voltage of the DC input voltage DCIV) is lowerthan the predetermined value PV, the comparator 2044 generates acomparison result CR. As shown in FIG. 1, after the comparator 2044generates the comparison result CR, a switch 2062 of the gate signalgeneration unit 206 can be turned on according to the comparison resultCR, resulting in an output resistor RO of the gate signal generationunit 206 being decreased. Because the output resistor RO of the gatesignal generation unit 206 is decreased, a sink current IS flowingthrough a gate pin 208 of the controller 200 is increased, wherein asshown in FIG. 1, the gate pin 208 is coupled to a power switch 102 ofthe primary side PRI of the power converter 100. In addition, the gatesignal generation unit 206 is further used for generating a gate controlsignal GCS to the power switch 102 according to a pulse width modulationsignal PWM, wherein the pulse width modulation signal PWM is generatedaccording to a feedback voltage VFB received by a compensation pin 210of the controller 200, the feedback voltage VFB corresponds to an outputvoltage VOUT of a secondary side SEC of the power converter 100, and thepower switch 102 is turned on and turned off according to the gatecontrol signal GCS. Thus, when the sink current IS flowing through thegate pin 208 of the controller 200 is increased and the gate controlsignal GCS is changed from high to low, because the sink current ISflowing through the gate pin 208 of the controller 200 is increased, thegate control signal GCS can be quickly changed from high to low (shownin FIG. 2), that is, the power switch 102 can be switched quickly,resulting in the efficiency of the power converter 100 being better.Although when the power switch 102 is switched quickly, electromagneticinterference of the power converter 100 is increased, theelectromagnetic interference of the power converter 100 can beeliminated easily because the DC input voltage DCIV is a low voltage(because the detection voltage VD is lower than the predetermined valuePV). Therefore, compared to the prior art, because the controller 200utilizes the switch 2062 to change the sink current IS according to thecomparison result CR, cost of the power converter 100 is not increasedsignificantly and the efficiency of the power converter 100 can beincreased. In addition, when the detection voltage VD (the dividedvoltage of the DC input voltage DCIV) is higher than the predeterminedvalue PV, the comparator 2044 does not generate the comparison resultCR, resulting in the switch 2062 of the gate signal generation unit 206being turned off. Because the comparator 2044 does not generate thecomparison result CR, the output resistor RO of the gate signalgeneration unit 206 is increased. Because the output resistor RO of thegate signal generation unit 206 is increased, the sink current ISflowing through the gate pin 208 of the controller 200 is decreased.

In addition, in another embodiment of the present invention, thecomparator 2044 generates the comparison result CR when the detectionvoltage VD (the divided voltage of the DC input voltage DCIV) is higherthan the predetermined value PV, resulting in the switch 2062 of thegate signal generation unit 206 being turned off (meanwhile, the switch2062 is a P-type metal-oxide-semiconductor transistor or a transmissiongate). Because the switch 2062 is turned off, the output resistor RO ofthe gate signal generation unit 206 is increased. Because the outputresistor RO of the gate signal generation unit 206 is increased, thesink current IS flowing through the gate pin 208 of the controller 200is decreased.

Please refer to FIG. 3. FIG. 3 is a diagram illustrating a controller300 for increasing the efficiency of the power converter 100 accordingto a second embodiment of the present invention. As shown in FIG. 3, thecontroller 300 includes an auxiliary pin 302, a comparison module 304,and the gate signal generation unit 206, wherein the comparison module304 includes a detection voltage generation unit 3042 and a comparator3044. As shown in FIG. 3, the auxiliary pin 302 is used for receiving anauxiliary voltage VAUX from a voltage divider 104 coupled to anauxiliary winding AUX of the power converter 100, wherein the auxiliaryvoltage VAUX corresponds to the DC input voltage DCIV of the primaryside PRI of the power converter 100, and the DC input voltage DCIVcorresponds to the AC input voltage ACIV inputted to the power converter100. The detection voltage generation unit 3042 included in thecomparison module 304 is coupled to the auxiliary pin 302 for generatingthe detection voltage VD according to the auxiliary voltage VAUX. Inaddition, the comparator 3044 included in the comparison module 304 isused for comparing the detection voltage VD with the predetermined valuePV to generate the comparison result CR. That is to say, when thedetection voltage VD is lower than the predetermined value PV, thecomparator 3044 generates the comparison result CR. In addition, asshown in FIG. 3, after the comparator 3044 generates the comparisonresult CR, subsequent operational principles of the controller 300 arethe same as those of the controller 100, so further description thereofis omitted for simplicity.

Please refer to FIG. 4. FIG. 4 is a diagram illustrating a controller400 for increasing the efficiency of the power converter 100 accordingto a third embodiment of the present invention. As shown in FIG. 4, thecontroller 400 includes a high voltage pin 402, an enable signalgeneration unit 404, and the gate signal generation unit 206. As shownin FIG. 4, the high voltage pin 402 can receive the DC input voltageDCIV from the primary side PRI of the power converter 100, wherein theDC input voltage DCIV corresponds to the AC input voltage ACIV inputtedto the power converter 100. The enable signal generation unit 404 iscoupled to the high voltage pin 402 for generating an enable signal EScorresponding to a duty cycle D of the gate control signal GCS accordingto the DC input voltage DCIV of the primary side PRI of the powerconverter 100 and the feedback voltage VFB corresponding to thesecondary side SEC of the power converter 100, wherein relationshipsbetween the duty cycle D of the gate control signal GCS, the DC inputvoltage DCIV, and the feedback voltage VFB can be determined accordingto equation (1).

$\begin{matrix}{{\frac{VOUT}{DCIV} = {{\frac{D}{1 - D} \times N} = \frac{{VFB} \times k}{DCIV}}}{\frac{VFB}{DCIV} = {\frac{D}{1 - D} \times \frac{N}{k}}}} & (1)\end{matrix}$

As shown in equation (1), k is a constant, VOUT is the output voltage ofthe secondary side SEC of the power converter 100, and N is a turnsratio of a winding of the primary side PRI of the power converter 100 toa winding of the secondary side SEC of the power converter 100. Inaddition, as shown in FIG. 4, the feedback voltage VFB is received by acompensation pin 210 of the controller 400, and the feedback voltage VFBcorresponds to the output voltage VOUT of the secondary side SEC of thepower converter 100. Therefore, the enable signal generation unit 404generates the enable signal ES to the gate signal generation unit 206when the duty cycle D of the gate control signal GCS is greater than apredetermined value, wherein as shown in equation (1), when the dutycycle D of the gate control signal GCS is greater than the predeterminedvalue, the DC input voltage DCIV is less than a predetermined voltagevalue. In addition, as shown in FIG. 4, after the enable signalgeneration unit 404 generates the enable signal ES to the gate signalgeneration unit 206, subsequent operational principles of the controller400 are the same as those of the controller 100, so further descriptionthereof is omitted for simplicity.

In addition, in another embodiment of the present invention, the enablesignal generation unit 404 generates the enable signal ES when the dutycycle D of the gate control signal GCS is less than the predeterminedvalue, resulting in the switch 2062 of the gate signal generation unit206 being turned off. Because the switch 2062 is turned off, the outputresistor RO of the gate signal generation unit 206 is increased. Becausethe output resistor RO of the gate signal generation unit 206 isincreased, a sink current IS flowing through a gate pin 208 of thecontroller 400 is decreased.

Please refer to FIGS. 1, 2, 5. FIG. 5 is a flowchart illustrating amethod for increasing efficiency of a power converter according to afourth embodiment of the present invention. The method in FIG. 5 isillustrated using the power converter 100 and the controller 200 inFIG. 1. Detailed steps are as follows:

Step 500: Start.

Step 502: The high voltage pin 202 receives the DC input voltage DCIVfrom the primary side PRI of the power converter 100.

Step 504: The detection voltage generation unit 2042 generates thedetection voltage VD according to the DC input voltage DCIV.

Step 506: If the detection voltage VD is less than the predeterminedvalue PV; if yes, go to Step 508; if no, go to Step 512.

Step 508: The comparator 2044 generates the comparison result CR.

Step 510: The gate signal generation unit 206 increases the sink currentIS flowing through the gate pin 208 of the controller 200, go to Step502.

Step 512: The gate signal generation unit 206 decreases the sink currentIS flowing through the gate pin 208 of the controller 200, go to Step502.

In Step 502, as shown in FIG. 1, high voltage pin 202 can receive the DCinput voltage DCIV from the primary side PRI of the power converter 100,wherein the DC input voltage DCIV corresponds to the AC input voltageACIV inputted to the power converter 100. In Step 504, the detectionvoltage generation unit 2042 of the comparison module 204 can generatethe detection voltage VD according to the DC input voltage DCIV of theprimary side PRI of the power converter 100, wherein the detectionvoltage VD is the divided voltage of the DC input voltage DCIV. Inaddition, in Step 508, the comparator 2044 of the comparison module 204generates the comparison result CR when the detection voltage VD (thedivided voltage of the DC input voltage DCIV) is lower than thepredetermined value PV. In Step 510, as shown in FIG. 1, after thecomparator 2044 generates the comparison result CR, the switch 2062 ofthe gate signal generation unit 206 can be turned on according to thecomparison result CR, resulting in the output resistor RO of the gatesignal generation unit 206 being decreased. Because the output resistorRO of the gate signal generation unit 206 is decreased, the sink currentIS flowing through the gate pin 208 of the controller 200 is increased.Thus, when the sink current IS flowing through the gate pin 208 of thecontroller 200 is increased and the gate control signal GCS is changedfrom high to low, because the sink current IS flowing through the gatepin 208 of the controller 200 is increased, the gate control signal GCScan be quickly changed from high to low (shown in FIG. 2), that is, thepower switch 102 can be switched quickly, resulting in the efficiency ofthe power converter 100 being better. Although when the power switch 102can be switched quickly, the electromagnetic interference of the powerconverter 100 is also increased, the electromagnetic interference of thepower converter 100 can be eliminated easily because the DC inputvoltage DCIV is a low voltage (because the detection voltage VD is lowerthan the predetermined value PV). Therefore, compared to the prior art,because the controller 200 utilizes the switch 2062 to change the sinkcurrent IS according to the comparison result CR, the cost of the powerconverter 100 is not increased significantly and the efficiency of thepower converter 100 can be increased. In addition, in Step 512, when thedetection voltage VD (the divided voltage of the DC input voltage DCIV)is higher than the predetermined value PV, the comparator 2044 does notgenerate the comparison result CR, resulting in the switch 2062 of thegate signal generation unit 206 being turned off. Because the comparator2044 does not generate the comparison result CR, the output resistor ROof the gate signal generation unit 206 is increased. Because the outputresistor RO of the gate signal generation unit 206 is increased, thesink current IS flowing through the gate pin 208 of the controller 200is decreased.

In addition, in another embodiment of the present invention, thecomparator 2044 generates the comparison result CR when the detectionvoltage VD (the divided voltage of the DC input voltage DCIV) is higherthan the predetermined value PV, resulting in the switch 2062 of thegate signal generation unit 206 being turned off (meanwhile, the switch2062 is a P-type metal-oxide-semiconductor transistor or a transmissiongate). Because the switch 2062 is turned off, the output resistor RO ofthe gate signal generation unit 206 is increased. Because the outputresistor RO of the gate signal generation unit 206 is increased, thesink current IS flowing through the gate pin 208 of the controller 200is decreased.

Please refer to FIGS. 3, 6. FIG. 6 is a flowchart illustrating a methodfor increasing efficiency of a power converter according to a fifthembodiment of the present invention. The method in FIG. 6 is illustratedusing the power converter 100 and the controller 300 in FIG. 3. Detailedsteps are as follows:

Step 600: Start.

Step 602: The auxiliary pin 302 receives the auxiliary voltage VAUX fromthe voltage divider 104 coupled to the auxiliary winding AUX of thepower converter 100.

Step 604: The detection voltage generation unit 3042 generates thedetection voltage VD according to the auxiliary voltage VAUX.

Step 606: If the detection voltage VD is less than the predeterminedvalue PV; if yes, go to Step 608; if no, go to Step 612.

Step 608: The comparator 3044 generates the comparison result CR.

Step 610: The gate signal generation unit 206 increases a sink currentIS flowing through a gate pin 208 of the controller 300, go to Step 602.

Step 612: The gate signal generation unit 206 decreases the sink currentIS flowing through the gate pin 208 of the controller 300, go to Step602.

As shown in FIG. 3, differences between the embodiment of the FIG. 6 andthe embodiment of the FIG. 5 is that in Step 602, the auxiliary pin 302can receive the auxiliary voltage VAUX from the voltage divider 104coupled to the auxiliary winding AUX of the power converter 100, whereinthe auxiliary voltage VAUX corresponds to the DC input voltage DCIV ofthe primary side PRI of the power converter 100, and the DC inputvoltage DCIV corresponds to the AC input voltage ACIV inputted to thepower converter 100; in Step 604, the detection voltage generation unit3042 can generate the detection voltage VD according to the auxiliaryvoltage VAUX. In addition, as shown in FIG. 6, after Step 604 isexecuted, subsequent operational principles of the embodiment of theFIG. 6 are the same as those of the embodiment of the FIG. 5, so furtherdescription thereof is omitted for simplicity.

Please refer to FIGS. 4, 7. FIG. 7 is a flowchart illustrating a methodfor increasing efficiency of a power converter according to a sixthembodiment of the present invention. The method in FIG. 7 is illustratedusing the power converter 100 and the controller 400 in FIG. 4. Detailedsteps are as follows:

Step 700: Start.

Step 702: The high voltage pin 202 receives the DC input voltage DCIVfrom the primary side PRI of the power converter 100.

Step 704: The enable signal generation unit 404 determines the dutycycle D corresponding to the gate control signal GCS according to the DCinput voltage DCIV and the feedback voltage VFB corresponding to thesecondary side SEC of the power converter 100.

Step 706: If the duty cycle D of the gate control signal GCS is greaterthan the predetermined value; if yes, go to Step 708; if no, go to Step712.

Step 708: The enable signal generation unit 404 generates the enablesignal ES.

Step 710: The gate signal generation unit 206 increases the sink currentIS flowing through the gate pin 208 of the controller 400, go to Step702.

Step 712: The gate signal generation unit 206 decreases the sink currentIS flowing through the gate pin 208 of the controller 400, go to Step702.

Differences between the embodiment of the FIG. 7 and the embodiment ofthe FIG. 5 is that in Step 704, the enable signal generation unit 404can determine the duty cycle D of the gate control signal GCS accordingto the DC input voltage DCIV of the primary side PRI of the powerconverter 100, the feedback voltage VFB corresponding to the secondaryside SEC of the power converter 100, and equation (1); In Step 708, whenthe duty cycle D of the gate control signal GCS is greater than thepredetermined value, the enable signal generation unit 404 generates theenable signal ES to the gate signal generation unit 206, wherein asshown in equation (1), when the duty cycle D of the gate control signalGCS is greater than the predetermined value, the DC input voltage DCIVis less than the predetermined voltage value, so the enable signalgeneration unit 404 generates the enable signal ES to the gate signalgeneration unit 206. In addition, as shown in FIG. 7, after Step 708 isexecuted, subsequent operational principles of the embodiment of theFIG. 7 are the same as those of the embodiment of the FIG. 5, so furtherdescription thereof is omitted for simplicity.

To sum up, the controller for increasing the efficiency of the powerconverter and the related method thereof utilize the comparison moduleto generate the detection voltage according to the DC input voltagecorresponding to the primary side of the power converter and to comparethe detection voltage with the predetermined value to generate thecomparison result, and utilize the gate signal generation unit toincrease the sink current flowing through the gate pin of the controlleraccording to the comparison result. In addition, the controller and themethod can also utilize the enable signal generation unit to generatethe enable signal corresponding to the duty cycle of the gate controlsignal according to the DC input voltage corresponding to the primaryside of the power converter and the feedback voltage corresponding tothe secondary side of the power converter, and utilize the gate signalgeneration unit to increase the sink current flowing through the gatepin of the controller according to the enable signal. Therefore, whenthe sink current flowing through the gate pin of the controller isincreased and the gate control signal is changed from high to low,because the sink current flowing through the gate pin of the controlleris increased, the gate control signal can be quickly changed from highto low. That is to say, the power switch of the primary side of thepower converter can be switched quickly, resulting in the efficiency ofthe power converter being better. Although when the power switch of theprimary side of the power converter is switched quickly, theelectromagnetic interference of the power converter is increased, theelectromagnetic interference of the power converter can be eliminatedeasily because the DC input voltage is a low voltage. Therefore,compared to the prior art, the present invention can increase theefficiency of the power converter without significant increase of thecost of the power converter.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A controller for increasing efficiency of a powerconverter, the controller comprising: an enable signal generation unitfor generating an enable signal corresponding to a duty cycle of a gatecontrol signal according to a DC input voltage corresponding to aprimary side of the power converter and a feedback voltage correspondingto a secondary side of the power converter, wherein the feedback voltagecorresponds to an output voltage of the secondary side of the powerconverter; and agate signal generation unit for changing a sink currentflowing through a gate pin of the controller according to the enablesignal, wherein the gate pin is coupled to a power switch of the primaryside of the power converter, and the gate signal generation unit isfurther used for generating a gate control signal to the power switch.2. The controller of claim 1, wherein the enable signal generation unitgenerating the enable signal corresponding to the duty cycle of the gatecontrol signal is the enable signal generation unit generating theenable signal when the duty cycle of the gate control signal is greaterthan a predetermined value.
 3. The controller of claim 2, wherein thegate signal generation unit changing the sink current flowing throughthe gate pin of the controller according to the enable signal is thegate signal generation unit increasing the sink current according to theenable signal when the duty cycle of the gate control signal is greaterthan the predetermined value.
 4. The controller of claim 1, wherein theenable signal generation unit generating the enable signal correspondingto the duty cycle of the gate control signal is the enable signalgeneration unit generating the enable signal when the duty cycle of thegate control signal is less than a predetermined value.
 5. Thecontroller of claim 4, wherein the gate signal generation unit changingthe sink current flowing through the gate pin of the controlleraccording to the enable signal is the gate signal generation unitdecreasing the sink current according to the enable signal when the dutycycle of the gate control signal is less than the predetermined value.6. The controller of claim 1, further comprising: a high voltage pin forreceiving the DC input voltage from the primary side of the powerconverter.
 7. A method for increasing efficiency of a power converter,wherein a controller applied to the method comprises a high voltage pin,an enable signal generation unit, and a gate signal generation unit, themethod comprising: the high voltage pin receiving a DC input voltagefrom a primary side of the power converter; the enable signal generationunit generating an enable signal corresponding to a duty cycle of a gatecontrol signal according to the DC input voltage and a feedback voltagecorresponding to a secondary side of the power converter, wherein thefeedback voltage corresponds to an output voltage of the secondary sideof the power converter; and the gate signal generation unit changing asink current flowing through the gate pin of the controller according tothe enable signal.
 8. The method of claim 7, wherein the enable signalgeneration unit generating the enable signal corresponding to the dutycycle of the gate control signal comprises: the enable signal generationunit generating the enable signal when the duty cycle of the gatecontrol signal is greater than a predetermined value.
 9. The method ofclaim 8, wherein the gate signal generation unit changing the sinkcurrent flowing through the gate pin of the controller according to theenable signal comprises: the gate signal generation unit increasing thesink current according to the enable signal when the duty cycle of thegate control signal greater than the predetermined value.
 10. The methodof claim 7, wherein the enable signal generation unit generating theenable signal corresponding to the duty cycle of the gate control signalcomprises: the enable signal generation unit generating the enablesignal when the duty cycle of the gate control signal is less than apredetermined value.
 11. The method of claim 10, wherein the gate signalgeneration unit changing the sink current flowing through the gate pinof the controller according to the enable signal comprises: the gatesignal generation unit decreasing the sink current according to theenable signal when the duty cycle of the gate control signal is lessthan the predetermined value.